The present invention relates to communications, and more particularly, to radio communications networks and terminals.
In a typical cellular radio system, wireless terminals (also known as mobile stations and/or user equipment units (UEs)) communicate via a radio access network (RAN) and one or more core networks. User equipment units may include mobile telephones (“cellular” telephones) and/or other processing devices with wireless communication capability, such as, for example, portable, pocket, hand-held, laptop computers, which communicate voice and/or data with the RAN.
The RAN covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks is also called a “NodeB” or enhanced NodeB (eNodeB), which can be abbreviated “eNB.” A cell area is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. The base stations communicate over the air interface operating on radio frequencies with UEs within range of the base stations.
In some versions of the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UTRAN, short for UMTS Terrestrial Radio Access Network, is a collective term for the Node B's and Radio Network Controllers which make up the UMTS radio access network. Thus, UTRAN is essentially a radio access network using wideband code division multiple access for user equipment units.
The Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM based radio access network technologies. In this regard, specifications for the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) are ongoing within 3GPP. The Evolved Universal Terrestrial Radio Access Network (E-UTRAN) comprises the Long Term Evolution (LTE) and System Architecture Evolution (SAE).
FIG. 1 is a simplified block diagram of a Long Term Evolution (LTE) RAN 100. The LTE RAN 100 is a variant of a 3GPP RAN where radio base station nodes (eNodeBs) are connected directly to a core network 130 rather than to radio network controller (RNC) nodes. In general, in LTE the functions of a radio network controller (RNC) node are performed by the radio base stations nodes. Each of the radio base station nodes (eNodeBs) 122-1, 122-2, . . . 122-M communicate with UEs (e.g., UE 110-1, 110-2, 110-3, . . . 110-L) that are within their respective communication service cells. The radio base station nodes (eNodeBs) can communicate with one another through an X2 interface and with the core network 130 through S1 interfaces, as is well known to one who is skilled in the art.
The LTE standard is based on multi-carrier based radio access schemes such as Orthogonal Frequency-Division Multiplexing (OFDM) in the downlink and Discrete Fourier Transform (DFT)-spread OFDM in the uplink. The OFDM technique distributes the data over a large number of carriers that are spaced apart at precise frequencies. This spacing provides the “orthogonality” in this technique which avoids having demodulators see frequencies other than their own. The benefits of OFDM are high spectral efficiency, resiliency to RF interference, and lower multi-path distortion.
FIG. 2 illustrates a resource grid for frequency and time resource elements (REs), where each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval. In the time domain, LTE downlink transmissions may be organized into radio frames of 10 ms, and each radio frame may consist of ten equally-sized subframes of length Tsubframe=1 ms, as illustrated in FIG. 3.
One or more resource schedulers in the LTE RAN 100 allocate resources for uplink and downlink in terms of resource blocks, where a resource block corresponds to one slot (0.5 ms) in the time domain and 12 subcarriers in the frequency domain. Resource blocks are numbered in the frequency domain, starting with 0 from one end of the system bandwidth.
Downlink transmissions are dynamically scheduled. More particularly, in each subframe, the base station transmits control information indicating to which terminals and on which resource blocks the data is transmitted during the current downlink subframe. This control signaling is typically transmitted in the first 1, 2, 3, or 4 OFDM symbols in each subframe. FIG. 4 illustrates a resource grid for a downlink subframe including 3 OFDM symbols on each subcarrier as control region.
The LTE standard uses hybrid-ARQ (hybrid Automatic Repeat reQuest), where, after receiving downlink data in a subframe, the wireless terminal attempts to decode the downlink data, and the wireless terminal reports to the base station whether the decoding was successful (ACK or acknowledge) or not (NAK or negative-acknowledge). In the event of an unsuccessful decoding attempt (i.e., the base station receives a NAK report from the wireless terminal), the base station can retransmit the erroneous data.
Uplink control signaling transmitted from the wireless terminal to the base station may include: (1) hybrid-ARQ acknowledgements for received downlink data; (2) terminal reports related to the downlink channel conditions, used as assistance for the downlink scheduling (also known as Channel Quality Indicator (CQI)); and (3) scheduling requests, indicating that a mobile terminal needs uplink resources for uplink data transmissions. If the mobile terminal has not been assigned an uplink resource for data transmission, the L1/L2 (Layer 1 and/or Layer 2) control information (e.g., including channel status reports, hybrid-ARQ acknowledgements, and/or scheduling requests) is transmitted in uplink resources (resource blocks) specifically assigned for uplink L1/L2 control information on the Physical Uplink Control Channel (PUCCH). Different PUCCH formats are used for different information. For example, PUCCH formats 1a/1b are used to report hybrid-ARQ feedback, PUCCH Formats 2/2a/2b are used to report of channel conditions, and PUCCH Format 1 is used for scheduling requests.
For a wireless terminal to transmit data over an uplink to a base station, the base station must assign an uplink resource to the wireless terminal on the Physical Uplink Shared Channel (PUSCH), and a PUSCH resource assignment is illustrated in FIG. 5. As shown, a reference signal may be transmitted in the middle SC-symbol in each slot. If the wireless terminal has been assigned an uplink resource for data transmission and at the same time instance has control information to transmit, the wireless terminal will transmit the control information together with the data on the PUSCH.
The LTE Rel-8 standard has recently been standardized, supporting bandwidths up to 20 MHz. 3GPP has initiated work on LTE Rel-10 to support bandwidths greater than 20 MHz and to support other requirements defined by IMT-Advanced Requirements. Another requirement for LTE Rel-10 is to provide backward compatibility with LTE Rel-8, including spectrum compatibility. This requirement may cause an LTE Rel-10 carrier to appear as a number of LTE carriers to an LTE Rel-8 terminal. Each such carrier can be referred to as a Component Carrier (CC) or as a cell. For early LTE Rel-10 deployments, it can be expected that there will be a smaller number of LTE Rel-10-capable terminals compared to many LTE legacy terminals. Therefore, it may be important to provide efficient use of the wide carrier by legacy terminals, such as by enabling legacy terminals to be scheduled in all parts of the wideband LTE Rel-10 carrier. One way to obtain this may be by means of Carrier Aggregation. Carrier Aggregation refers to an LTE Rel-10 terminal being configured to receive multiple CCs, where each CC has, or at least has the possibility to have, the same structure as a Rel-8 carrier. The same structure as Rel-8 implies that all Rel-8 signals, e.g. (primary and secondary) synchronization signals, reference signals, system information, etc. are transmitted on each carrier. FIG. 6 graphically illustrates an exemplary 100 MHz Carrier Aggregation of five 20 MHz CCs.
Referring to FIG. 6, the number of aggregated CCs as well as the bandwidth of the individual CC may be different for uplink and downlink. A symmetric configuration refers to the case where the number of CCs in downlink and uplink is the same, whereas an asymmetric configuration refers to the case that the numbers of CCs in downlink and uplink are different. It is important to note that the number of CCs offered by the network may be different from the number of CCs seen by a terminal. For example, a terminal may support more downlink CCs than uplink CCs, even though the network offers the same number of uplink and downlink CCs.
Uplink power control is used both on the PUSCH and on PUCCH. The purpose is to provide that the mobile terminal transmits with sufficiently high power but not too high power since the latter may increase interference to other users in the network. In both cases, a parameterized open loop combined with a closed loop mechanism may be used. Roughly, the open loop part may be used to set a point of operation, around which the closed loop component may operate. Different parameters (targets and ‘partial compensation factors’) for user and control plane may be used. For further description of PUSCH and PUCCH power control, see sections 5.1.1.1 of 3GPP 36.213, Physical Layer Procedures.
To control the UE's (User Equipment's) UL (Uplink) power, the eNB (Evolved Node B) base station may use TPC (Transmission Power Control) Commands which will order the UE (User Equipment) to change its transmission power either in an accumulated or absolute fashion. In LTE Rel-10, the UL power control is managed per Component Carrier. As in Rel-8/9 PUSCH and PUCCH power control is separate. In LTE Rel-10, the PUCCH power control will only apply to the Primary Component Carrier (PCC) since this is the only UL CC configured to carry PUCCH.
Because the UE does not provide ACK/NACK responses to TPC commands from the eNB base station, the eNB base station cannot be sure that the TPC commands are received by the UE. Because the UE may falsely decode the PDCCH as including a TPC command, counting used TPC commands cannot be used to reliably estimate a current output power from the UE. In addition, the UE may also compensate its power level autonomously (based on path-loss estimates), and these autonomous adjustments may be unknown to the eNB base station. For these reasons, the eNB base station may need to receive PHR (Power Headroom Report) reports regularly to make competent scheduling decisions and control the UE UL power.
Accordingly, the UE may be required to compute Power Headroom Reports for each component carrier being used for uplink transmissions from the UE to the eNB. Notwithstanding known techniques of reporting power headroom, there continues to exist a need for improved power headroom reporting providing increased efficiency.